Magnetic chucks



ug. l5, i967 CS1-EAD 3,336,551

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y bnmmmm@ new a W W H um n@ ww WN MN Mmmm www @www www qu 5S S @n ww 0% United States Patent O 3,336,551 MAGNETIC Cil-BUCKS` Clifford Stead, North Smithfield, RJi., assigner to The Taft-Peirce Manufacturing Company, Woonsocket, Rdf., a corporation of Rhode Island lliiled Aug. 5, 1964, Ser. No. 387,604 1l Claims. (Cl. 335-295) The present invention relates to work holding magnetic chucks of the permanent magnet type.

Many of such `chucks have a chambered casing or frame structure in which is housed `shiftable pack means embodying spaced permanent magnet and steel conductor elements slidably associated with a superposed work supporting faceplate closing the top of the chamber and made up of spaced pole .pieces for cooperative general alignment with the magnet and conductor elements in a work holding or on position of the pack and shunting staggered relation thereof in another work release or off pack position.

A Iconventional form of such chucks provides the chambered casing or frame structure as a rectangular assembly of a flat paramagnetic or steel bottom plate and an open box sidewall frame of diamagnetic material, such as aluminum, bolted to the bottom plate. The at bottom of the shiftable pack and the top of the steel bottom plate are carefully machined for close fitting to allow the latter to serve as an effective keeper for the magnet pack in the different relative positions and heavy grease is interposed to facilitate relative sliding action. The bottom face of the work suporting faceplate and the top face of the shiftable pack are also carefully machined and heavy grease interposed for a like purpose. These respective grease gaps are limited toa maximum clearance of about 0.003 to avoid undue weakening of the strength of the magnetic holding power. Even with such careful machining there is a hazard that bottom edges of the faceplate pole pieces and opposed top edges of the magnet pack bars and intervening conductor bars will interfere or catch in the longitudinal shifting of the pack if this clearance is appreciably less. Also carefully machined guide lands are provided on the inside faces of the sidewalls, and ropposed side edges of the shiftable pack must be carefully machined for close fitting thereto and easy relative sliding action without catching and undue play. The meticulous machining required and the assembly procedure necessitated are costly and undesirably increase production costs,

It is an object of the present invention to eliminate such undue costs and to increase the openating effectiveness by improved design Whiich permits the casing or frame structure to =be made as a unitary fa-bricated structure of diamagnetic material, such as aluminum, by a simple sand or die casting, with the necessary bottom keeper being carried 4above the frame bottom plate by the bottom of the shiftable pack thereby eliminating undue friction therebetween and the need for reducing the latter by an interposed layer of drag imposing heavy grease. This one piece frame or base structure provides greater rigidity which assures more secure anchorage in a flat disposition. In prior constructions where lthe function of the keeper was served by the fixed steel bottom frame plate there was tendency for the top faceplate to be deflected downwardly by the magnetic force exerted by the intervening magnet pack as it attempted to close gaps in the magnetic path within the vertical spacing of the faceplate and bottom frame keeper plate as dictated by the frame sidewall structure. Such tendency for faceplate deflection occurred not `only in the olf position of the magnet pack regardless of conditions but also in the on pack position when a relatively narrow workpiece was located along the longitudinal central zone of the faceplate. The

3,336,551 Patented Aug. 15, 1967 support of the keeper by the magnet pack in the present magnetic chucks eliminates these diiiiculties. The necessity of abutted sliding faces and meticulous machining thereof is avoided by substituting for the grease layer interposed between the bottom face of the superposed work supporting faceplate and the opposed top face of the shiftable pack effective slide promoting plastic sheeting of high lubricity, and providing effective guidance of the reciprocated pack solely by simple interfitting glide or riding means on these opposed faces.

In such conventional forms of chucks the .pole pieces of the work supporting faceplate, in the form of transverse steel bars, usually are spaced apart by intervening strips `of diamagnetic material, lsuch as epoxy, brass, etc., with longitudinal tie rods clamping the lateral sandwich of parts together. The shiftable pack may be made up of an alternate arrangement of transverse permanent magnet bars and intervening conductor bars of panamagnetic material, such as steel,l for magnetic iiux conduction, spaced from each other by interposed strips of diamagnetic material, such as brass, with this lateral sandwich of parts clamped together by longitudinal tie rod means. Even though great care be taken in providing such bars and :strips in certain thicknesses in an attempt to assure uniform spacings of elements in the superposed plate and shiftable pack for attaining ideal alignment thereof in the work holding position and staggered relation in the release position, it is frequently characteristic of such chucks that while the ideal alignment is attained between the `opposed elements at one end of the chuck in the work holding position of the pack an accumulation of slight errors progressively along the lateral sandwiches of parts causes appreciable misalignment in the holding position to reduce the efliciency of the work holding force. The staggered relation of the opposed elements in the release position of the pack also suffers for the same reason. In order to minimize this effect it is a practice to provide the frame structure with adjustable stop means, such as stop screws, to limit pack throw in the two positions and to ignore the :cumulative errors causing misalignments and the alternate faulty staggered relations by attaining the -best possible mean alignments with careful and tedious adjustments of the stop screws.

It is another object of this invention to provide in the improved chucks unique throw equipment which can be simply adjusted in an effective manner to shift at will the terminals of the pack slide stroke along the work holding plate to any of a plurality of locations of adjustment in minute increments by greatly multiplied increments of adjusting action. For this purpose the present invention embodies in the pack reciprocating mechanism eccentric means which by relatively large increments of simple angular adjustment shifts in minute increments the axis of rotary throw equipment thereof along the path of slide of the pack. Structural characteristics and variations thereof will be apparent from the following descriptive disclosure and the drawings described therein.

A further object of the invention is to provide structural embodiments of the device which may be readily and economically constructed and assembled, and which permit effective adjustment with ease and etiicient use and operation thereof.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. l is a perspective view, with parts broken away, of a magnetic chuck of the permanent magnet type embodying the improvements of the present invention, illustrating therein a portion of a workpiece being supported thereon and held by its magnetic field as produced with the pack thereof shifted to its work holding or on position;

FIG. 2 is an exploded view of the chuck device illustrated in FIG. 1, showing parts in the same relative positions and others manipulated to distorted disposition for illustrative understanding;

FIG. 3 is a top plan view, with parts broken away and in section, of the chuck device illustrated in FIGS. l and 2, with the shiftable pack located in the work holding or on position;

FIG. 4 is a longitudinal section taken substantially along line 4-4 of FIG. 3, with parts broken away;

FIG. 5 is an enlarged transverse sectional view taken substantially along line 5-5 of FIG. 4, with parts broken away;

FIG. 6 is an enlarged longitudinal sectional View taken substantially along line 6-6 of FIG. 5, with parts broken away, showing the relative alignment of parts of the work supporting faceplate and the shiftable pack when the latter is in the same Work holding position;

FIG. 7 is a sectional detail, with parts broken away, of the left end portion of FIG. 6, showing the relative positions of parts in the work release position of the shiftable pack relative to the work supporting faceplate; and

FIG. 8 is an exploded phantom perspective of parts of both the work supporting faceplate and the shiftable pack of the chuck device illustrated in FIGS. 1 to 7 incl., depicting with greater clarity certain structural details thereof.

Referring to the drawings, in which like numerals identify similar parts throughout, it will be seen that an ernbodiment of the magnetic chuck of the present invention includes a casing base or frame structure 10', a work supporting faceplate structure 11 and a shiftable permanent magnet pack 12, and the embodiment therein of unique pack reciprocating mechanism 13.

The casing base or frame structure 10 preferably is in the form of a one-piece casing pan of diamagnetic material, such as aluminum, provided with integral opposed sidewalls 14 and 15 and integral opposed end walls 16 and 17 flanking therein a chamber recess 18 and together with an integral bottom wall 19 thereof defining a rectangular bottom section of a chamber in which the shiftable pack 12 is ultimately housed.

As will be seen from FIGS. 3, 4 and 6 to 8 incl., the Work supporting faceplate structure 11 is of general rectangular shape in the form of a lateral sandwich of parts fixed together and includes a left end plate 20, a right end plate 21 and a plurality of pole pieces 22 all in the form of transverse bars of paramagnetic material, which may be made of mild steel. These transversely-extending bar elements of the top faceplate structure 11 are suitably separated or spaced laterally by intervening diamagnetic strips 23 which may be formed of brass. Opposed abutted faces of the intervening spacing brass strips 23, the transverse left and right end plates 20` and 21 and the transverse pole pieces 22 (four of which are identified by the numeral 122 because of a minor variation thereof hereinyafter explained) preferably are brazed or cemented together to form a unitary fixed assembly, although other suitable means, such as tie rods, may be employed for this purpose. Epoxy cement may be used to cement these faceplate elements together. The resulting work supporting faceplate structure or assembly 11 has a top work supporting surface 24 and an inner or bottom face 25.

The Work supporting faceplate structure 11 preferably is provided with a left end stop strap 26 mounted to left end plate 20 by means of screws 27 preferably inserted through vertical slots 28 in this end stop strap for permitting adjustment of the height of the top edge of the latter, as will be understood from FIGS. 1 to 5 incl. A back stop strap 29 is mounted to the far longitudinal side edge of the work supporting plate structure 11 -in a similar manner, such as by screws 30, as will be understood also from FIGS. 1 to 5 incl. Vertical slots 31 in this back stop strap 29 through which anchoring screws 30 are inserted also permit the -desired elevational adjustment of the top edge of this back stop strap. The back stop strap is of paramagnetic material such as stainless steel. The cooperative function of the end stop strap 26 and the back stop strap 29 is indicated in FIGS. 1 and 6 wherein is shown placement of a paramagnetic or steel workpiece 32 upon the top surface 24 of the work supporting faceplate structure 11, with edges thereof abutted against the end stop strapA and the back stop strap for holding it securely in position while grinding or machining operations are performed thereon.

The shiftable magnetic pack 12 is also in the form of a lateral sandwich of parts which include a plurality of transversely-extending permanent magnet bars 33 having their top edges 34 constituting the north poles thereof and their bottom edges 3S constituting the south poles thereof, as will also be understood from FIGS. 3, 4 and 6 to 8 incl. The bar magnets 33 are alternated with conductor bars 36, 136, 236 and 336 of paramagnetic material, such as steel. The opposed faces of the magnet bars 33 and the conductor bars 36 are intervened and spaced by strips 37 of diamagnetic material, such as brass or other suitable non-magnetic substance. Preferably the bars 33 and 36-336 and the intervening strips 37 of the shiftable pack 12 are secured together by brazing opposed side faces to each other, although other suitable means may be employed as in the case of the work supporting faceplate sandwich 11, and these bars and intervening strips preferably may be of equal heights. To the botto-m of the shiftable pack sandwich 12 is secured a keeper plate 38 to transfer lines of magnetic flux between the conductor bars 36-336 and the south pole edges 3S of the magnet bars 33, and the bottom face of this keeper bar is spaced appreciably above and out of contact with the top of the casing bottom wall 19 to avoid frictional contact therebetween. While the keeper plate 38 may be so mounted to the bottom face of the shiftable pack 12. by any suitable mechanical anchoring means the latter lis not necessary since the magnetic fields of the permanent magnet bars 33 at the bottom south pole edges 35 thereof will effectively hold this keeper tightly clamped in position.

The conductor bars 136 at the right and left hand ends of the shiftable pack 12 need be only one half the thickness of the shunt bars 36 in the interior of the pack since the former need carry only one half of the lines of magnetic flux that are transferred by the latter. The elements of the shiftable pack 12 comprising the permanent magnet bars 33, the steel conductor bars 36-336 and the intervening brass strips 37 all have their top edges disposed in a common plane together to constitute a flat top face 39 opposed to the bottom face 25 of the work supporting faceplate assembly 11. These opposed faces 39 and 25 are respectively disposed substantially in parallel lateral planes and one is intended to slide relative to the other, the action effected by longitudinal reciprocative shift of the pack 12.

Since the shiftable magnetic pack 12 is to be guided in its longitudinal reciprocation in a manner avoiding contact between side edges thereof and any sidewall portions of the recessed casing base or frame structure 10 such cooperative reciprocation guiding means is uniquely and conveniently provided in the form of interfiting relative sliding means carried by or formed in the opposed flat plate bottom face 25 and shiftable pack top face 39. This guiding means is provided in a form which limits reciprocation of the pack to straight line motion and comprises channel means in one of the opposed faces 25 and 39 and projecting means ou the other thereof freely riding in this channel means. In a preferred form of this guiding means two of the conductor bars, such as the second from the left end of the pack at 236 and the second from the right end of the Ipack at 336, as will be best understood from FIGS. 3, 4 and 6, are equipped with upwardly-projecting guide pins 40, which may be of brass, high lubricity plastic or other suitable material. While the bottom face 25 of the work supporting faceplate 11 may be provided with a longitudinal channel extending substantially the full length thereof, in sections of which the guide pins 40 ride freely, such channel sections 41 are economically provided as relatively short, elongated notches in the bottom edges of a pair of pole pieces 122 at each end of the work supporting faceplate assembly 11, as will be undersood from FIGS. 2 to 6 incl. It is preferred to anchor each guide pin 40 in each of the two conductor bars 236 and 336 by a slip fit within a vertical drilled through hole 42, with the bottom end 4-3 of each pin resting upon keeper plate 38, as will be seen from FIGS. 4 and 5.

In substitution for the thick layer of heavy grease conventionally interposed between the top face of the shiftable magnetic 'pack and the bottom face of the work supporting faceplate assembly there is interposed between these opposed faces 39 and 25 of the embodiment of the device of the present invention illustrated in the drawings slide promoting means spacing them a minimum distance apart which comprises thin, tough, long wearing plastic sheeting of low friction and high lubricity. In order to avoid undue weakening of the magnetic eld transferred from the shiftable magnets 33 through the plate pole pieces 22 and 122 into the back through the workpiece 32 for effectively holding the latter in position on the chuck such plastic sheeting is to be of minimum thickness and, in any event, should be no greater than about 0.003 thick. The use of this spacing plastic sheeting which provides the desired ready sliding of the shiftable pack face 39 relative to the opposed bottom face 25 of the work supporting faceplate may be of any desired shape and cover any desired extent of these opposed faces. However, frictional drag is further minimized if it is employed in relatively narrow strips transversely spaced apart. Also, this transverse spacing of such strips provides an intervening central zone in which the intertting guide means, Iconsisting of the guide pins 40 and the slots 41 slidably receivig them, are located. Such slide promoting strips 44 may be in the form of a pair thereof, as will be seen from FIGS. 2 to 5 incl.

These transversely-spaced interposed strips 44 may be of any plastic material which satisfies the requirements of thickness and long wearing characteristic of the sliding surface, and low friction and high lubricity in the latter. While nylon may be satisfactory perfluoroalkane nesin, such as polymers of tetrauoroethylene, a common form of which is marketed under the trade name of Tellon, may -be preferred. Strips 44 of plastic sheeting may be readily anchored to either the Iunderface 25 of the work supporting faceplate assembly 11 or the. top face 39 of the shiftable pack 12 by interposed cement and, for this purpose, it may be in the form of sections of Teflon tape having a single tacky cement-bearing side, which may be readily obtainable in roll form. It is indicated in FIG. 2 that the tacky face 45 of the strips of tape 44 are laid down for adhesion to the top face 39 of the shiftable pack 12. Since the bottom of the shiftable pack 12 and the steel keeper plate 38 carried thereby are to be spaced upwardly from the top surface of the bottom Wall 19 of the recessed casing base 10 to avoid frictional contact therebetween the magnetic field or lines of flux which transverse the space between the opposed shiftable pack top face 39 and work supporting plate bottom face 25 is simply relied on to keep these faces as close together as possible, as is permitted by the thin strips of tape 44. Since Teflon plastic material has high lubricity and long wearing quality the guide pins 40 may also be advantageously formed thereof.

In initially assembling the parts of the chuck the work Supporting faceplate structure 11 is rested upon the antifriction strips 44 carried by the shiftable magnetic pack 12 and keeper plate 3S is applied to the bottom of the latter, and this stack of parts is made a magnetized subassembly. This magnetized sub-assembly is placed upon casing base 10 with the magnetic pack 12 and its keeper plate 38 nested in the recess 18, and the work supporting faceplate structure 11 is then anchored to the top edge of the latter by any suitable means, such as a plurality of machine screws of the fllister head type, the nature, structural features and arrangement of which will be best understood from FIGS. 3 and 4. As a result, the shiftable magnetic pack 12 is protectively confined in a closed chamber.

The shiftable pack 12 is designed to be manually reciprocated by suitable throw mechanism 13 -between its work holding on position (illustrated in FIG. 6) and its work release off position (illustrated in FIG. 7). This means 13 to reciprocate the magnetic pack 12 laterally between these two positions, and thus its permanent magnet bars 33 and steel conductor bars 36 relative to the faceplate pole pieces 22 and 122, preferably is in the form of manually operable rotary cam means which comprises a cylindrical through hole 46 formed in a boss 47 made integral with the casing base sidewall 14, as will be best understood .from FIGS. 3 to 5 incl. This rotary cam means also comprises a cylindrical bushing or bearing sleeve 48 rotatably mounted in the through hole 46, and it has an enlarged outer or head end 49 extending -beyond the outer face 50 of the boss 47 for engagement exterior of the casing base structure 10 to be rotated to a circumferentially adjusted position. For this purpose the enlarged head end 49 of the sleeve 48 preferably is flatted off on opposite sides at 51, as will be Seen from FIGS. 1 to 3 incl., Kfor ready engagement by a Spanner wrench to permit angular adjustment thereof in the transverse hole 46. The bushing or bearing sleeve 48 has a cylindrical through bore 52 eccentrically located therein with respect to thel cylindrical outer surface of this sleeve, and a manually rotatable shaft 53 is rotatably supported in this longitudinal through bore (FIGS. 3 to 5 incl). The bearing sleeve or bushing through which the throw shaft 53 is journaled may be a bronze Oilite sleeve or self-lubricating, graphite-impregnated, bronze bushing. The projecting outer end of the rotatable shaft 53 has a transverse through hole 54 into which is anchored a transverse manual handle 55 by any suitable means, such as a conventional crimped or corrugated steel tolerance ring. Handle 55 carries a manually engageable knob 56 which may be anchored thereto by similar means.

Inner end 57 of the manually rotatable shaft 53 carries eccentric means which engages the opposed edge of the shiftable pack 12 so that manual rotation of this shaft will reciprocate the latter between its work holding and release positions. The eccentric means on the shaft inner end 57 may be in the form of a crank pin 58 and a slide block 59 rotatably carried by the inner end thereof. The end of the conductor bar 336 of the shiftable pack 12 which is .opposed to the inner end 57 of the manually rotatable shaft 53 is notched or cut away to provide a recess 60 in which the slide block 59 may freely ride up and down (see FIGS. 3, 5 and 6). The brass spacer strips 137 which flank opposite side faces of the conductor bar 336 are also of full depth of the magnetic pack and thus close off opposite sides of the slide block recess 60, thereby providing opposed parallel flat guide faces for the up and down motion of the Islide block 59, as will be understood from FIGS. 3, 5 and 6. It is indicated in FIG. 3 that the crank pin 58 is mounted to the inner end 57 of the manually rotatable shaft 53 at a point radially offset from or eccentric of the axis of this shaft by providing the shaftinner end with an offset bore 61 in which pin inner end 62 is press-fitted. Thus, since crank pin 58' is fixedly carried at a radially offset point on the shaft inner end 57 it is journaled in a hole in slide block 59 for relative rotation. It is to be understood that the slide block 59 may carry the crank pin 58 which in turn may be rotatably yconnected at an eccentric point to the shaft inner end 57. Since the slide block 59 is, in the preferred form, to be journaled to the crank pin 58 and it is to be mounted between the brass spacer strips 137 for up and down guided sliding motion between the full line position at 59 and the dotted line position 159, shown in FIGS. and 6, it is preferably fabricated from steel, as is crank pin 53.

It is virtually impossible, as a practical matter, to so produce in accurate thickness the pole pieces 22 and 122, and the intervening spacing strips 23 of the work supporting faceplate assembly 11, as well as the permanent magnets 33, the conductor bars 36, 236 and 336 alternated therewith and the interposed spacing strips 37 and 137 of the shiftable pack 12, and so braZe or cement them together in opposed side face relation as to attain true alignment of the pole pieces with the magnets in the work holding position of the pack throughout the longitudinal extents of the faceplate and pack. Very minor dimensional variations are cumulative from one end to the other of either or both the faceplate assembly 11 and the shiftable pack structure 12, so that while true alignment may be attained initially at one end appreciable misalignment may occur at the other. It has been previously proposed to solve this problem to a practical extent by providing adjustable stop screws at opposite ends of the throw of the shiftable pack 12 and initially carefully adjusting them so that the best over-all desired alignments of pole pieces of the plate assembly 11 and the magnets and alternated conductor bars of the pack 12 are attained in both the work holding and release positions, i.e., a relative mean register of these parts which assures the best possible operating characteristics. Initial adjustment of such stop screws to attain this optimum of mean adjustment of alignments is very difficult to attain. The throw mechanism 13 solves this problem in a simple manner.

With the manual operating handle 55 in the work holding or on position shown in full lines in FIGS. l to 5 incl. the shiftable pack 12 will be adjusted longitudinally in minute increments by rotating the eccentric bushing or bearing sleeve 48 with a spanner wrench engaging its flats 51, until the optimum mean adjustment is attained. Such rotation of the eccentric sleeve 48 shifts the axis of the shaft 53 and its crank pin 58 longitudinally so that the slide block 59 will be translated with the latter to effect the desired pack shift. Considerable angular rotary adjustment of the eccentric sleeve 48 by the spanner wrench effects only a minute longitudinal adjustment of the pack due to the multiplying characteristic of this mechanism. Upon attainment of the proper angular adjustment of eccentric bearing sleeve 48 set screw 63 in boss 47 is tightened to hold it in the adjusted position (FIG. 5).

After this mean adjustment of the shiftable pack 12 has been attained stop screws 64 and 65, which are respectively threaded in internally threaded holes in casing end walls 16 and 17, are adjusted to dictate the on and off positions of the pack. Stop screw 64 is screwed inward until its inner end is brought to abutment of the outer tace of the left hand end condu-ctor bar 136 of the shiftable pack 12, as viewed in FIG. 6, when the pack is in its predetermined best on position. Then the shiftable pack 12 is thrown back to the best off position thereof and stop screw 65 is screwed inward to abutment of its inner end with the outer face of the right end conductor bar 136. It is a simple matter merely to screw these stop screws into abutment of the opposite ends of the packs in these respective positions to attain the best possible presetting of the shiftable magnetic pack 12 and the proper throw thereof for maximum operative eiciency.

In operation of the embodiment of the permanent magnet chuck illustrated in the drawings it will be seen from FIG. 6 that with the shiftable magnetic pack 12 thrown to the left to abutment of the left end conductor bar 136 against the inner end of stop screw 64, as attained by swinging the manual handle 55 and its knob 56 to the full line position illustrated in FIGS. 1 to 5 incl., the permanent magnets 33 of the pack are theoretically aligned with the pole pieces 22 and 122 of the work supporting faceplate structure 11. A portion of a paramagnetic or steel workpiece 32 is shown supported upon the top surface 24 of the faceplate structure 11 with abutment of the left side thereof against the end stop strap 26 and the back thereof against the longitudinal stop strap 29, as may be more apparent from the showing in FIG. 1. It is indicated in FIG. 6 that in the left end sections of the work supporting faceplate structure 11 and the shiftable pack 12 that magnetic lines of flux emanating from the top north pole edges 34 of the permanent magnets 33 traverse the pole pieces 22 thereabove to extend into the workpiece 32, serving as a keeper, and then turn back through adjacent pole pieces 22 and the end plate Ztl to be carried down through the conductor bars 136, 236 and 36 of the pack for transfer by the keeper plate 38 to the south pole edges 35 of the permanent magnets. In this on position of the shiftable pack 12 the magnetic flux lines which have paths through the workpiece 32 securely clamp the latter to the top surface 24 of the work supporting faceplate structure 11 to permit machining or grinding operations to be performed thereon while so clamped securely in position. It will be noted that in this work holding or on position of the shiftable pack depicted in FIG. 6 that the right end conductor bar 136 is spaced a distance X from the inner end of the stop screw 65 carried by the right end of the casing base structure 10. It is also shown in FIG. 6 that the thickness of one ofthe brass spacing strips 37 and an adjacent permanent magnet bar 33 or a conductor bar 36 which is of the same thickness constitutes a longitudinal unit dimension Y. The throw stroke X as determined by the presetting of the stop screws 64 and 65 is equal to one half of the unit dimension Y.

If now the manual handle 55 and its engaging knob 56 are rotated clockwise as viewed in FIGS. l to 5 incl. the shaft 53 will be rotated thereby in the same direction thereby within the bore 52 of the eccentric bushing or bearing sleeve 48 to swing the crank pin 58 upward and toward the right. The crank pin 58 carries through its arcuate path the slide block 59 which is thereby moved upwardly to the dotted line position 159 (FIGS. 5 and 6) between the projecting ends of the brass spacer strips 137 flanking the recess 60, and then downwardly therebetween in following the arcuate path described by the crank pin 58. As a result, the glide projecting portions of the spacing strips 137 between which the slide block 59 is moved up and down are caused to be moved to the right to carry with them the remainder of the shiftable pack 12 until the right end conductor bar 136 is brought to abutment of the inner end of the stop screw 65 which dictates the release or off position of the shiftable pack. This longitudinal translation of the shiftable pack 12 through the throw or stroke distance X is accomplished in rotating the manual handle 55 and its knob 56 clockwise through an angle of about The staggered relation of the permanent magnets 33 with respect to the interposed conductor bars 236 and 36, as well as the end conductor bar 136, is shown in FIG. 7. It is therein indicated that approximately one half of the magnetic ux lines emanating from the north pole 34 of the far left permanent magnet 33 will now be shunted through the far left pole piece 22 to travel down through the pack conductor bar 136 and then to pass through the 9 keeper plate 38 to the south pole bottom edge 35 of this permanent magnet. The remaining magnetic flux lines emanating from this permanent magnet north pole 34 will travel up into and be shunted through the next adjacent pole piece 122 to pass down through the next adjacent conductor bar 236 for shunting back through the keeper plate 38 to the same south pole 35 of this first permanent magnet. The paths of t-ravel of the flux lines of the magnetic fields of the next succeeding permanent magnets 33 are indicated in FIG. 7 which illustrates that the pole pieces 22 and 122 of the work supporting faceplate assembly 11 and the keeper plate 38 cooperate with the conductor bars 36 and 236 so that practically none of the magnetic iiux lines travel upwardly through the pole pieces to traverse any portions of any paramagnetic workpiece that may be resting upon the top surface 24 of the faceplate structure 11. In this release or off position of the shiftable pack 12 there is thus no magnetic holding or clamping of any paramagnetic body resting upon the plate assemby 11 since the staggered relation of the permanent magnets 33 and the conductor bars 36, 136 and 236 of the shiftable pack relative to the faceplate pole vpieces 22 and 122 provides effective shunt paths for the magnetic flux lines of the pack permanent magnets 33 immediately about the latter.

It Will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the `above description or shown in the Iaccompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, .and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a magnetic chuck of the permanent magnet type, comprising (a) la casing base structure having a recess therein defined by an inside bottom Wall and inside sidewalls,

(b) a work supporting faceplate mounted on said base structure and covering the recess therein with said faceplate including an assembly of laterally-spaced pole pieces of paramagnetic material, 'said faceplate having an inner face arranged substantially in a latteral plane,

(c) a magnetic pack of the permanent magnet type reciprocatively mounted for lateral movement in said -recess free of any Contact with any opposed portions of said bottom and side walls defining the latter, with said pack including an assembly of laterally-spaced permanent magnets cooperatively larranged with respect to said faceplate pole pieces in a lateral work holding position of said pack with said pack having a face disposed in a Asubstantially lateral plane op-` posed to said inner face of said faceplate for lateral reciprocation relative to the latter, and

(d) means to reciprocate said pack laterally between the work holding position and another position of work release relative to said faceplate pole pieces; the improvement comprising (e) means guiding free reciprocation of said pack in the base structure recess which eliminates any frictional sliding contact between any portions of and fixedly mounted on the inside bottom and side walls of the base structure recess and opposed portions of said pack, and

(f) slide promoting means interposed between said faceplate and pack opposed faces spacing them a minimum distance apart comprising thin, tough, long wearing diamagnetic plastic sheeting of low friction I and high lubricity, while magnetic attraction between said faceplate `and pack maintain the opposed faces of said faceplate and pack urged toward each other on opposite sides of said plastic sheeting.

2. The magnetic chuck of claim 1 in which opposed areas of the opposed faces of said faceplate and pack are free of portions of said interposed plastic sheeting with these sheeting-free areas having at least one pair of opposed portions extending parallel to the direction of yrelative reciprocation, said pair of opposed sheeting-free area portions that are parallel to the reciprocation direction being provided with said guiding means in the form of intertting relative sliding means.

3. The magnetic chuck of claim 2 in which said guiding means limits reciprocation of said pack to straight line motion and is being provided as channel means in one of said faces and projecting means on the other of said faces riding in said channel means, said interposed plastic sheeting being in the form of a plurality of transversely-spaced strips located laterally to opposite sides of said interfitting channel and projecting guiding means.

4. In a magnetic chuck of the permanent magnet type, comprising (a) a casing base structure having a recess therein,

(b) a work supporting faceplate mounted on said base structure and covering the recess therein with said faceplate including an lassembly of laterally-spaced pole pieces of paramagnetic material, said faceplate having an inner face arranged substantially in a later- .al plane,

(c) a magnetic pack of the permanent magnet type reciprocatively mounted for lateral movement in said recess with said pack including an assembly of laterally-spaced permanent magnets cooperatively arranged with respect to said faceplate pole pieces in a lateral work holding position of said pack with said pack having a face disposed in a substantially lateral plane opposed to said inner face of said faceplate and lateral reciprocation relative to the latter, and

(d) means to reciprocate said pack laterally between the work holding position and another position of work release relative to said faceplate pole pieces; the improvement comprising (e) guide means to limit reciprocation of said pack to straight line motion, and

(f) said means to reciprocate said pack being manually operable rotary cam means comprising (i) means defining a cylindrical through hole in a section of said casing structure which serves as a sidewall of said recess,

(ii) a cylindrical bearing sleeve rotatably mounted in said hole and having an outer end engageable from the exterior of said casing base structure for rotating said bearing sleeve to a circumferentially adjusted position, said sleeve having a cylindrical through bore eccentrically locater therein with respect to the cylindrical outer surface of said sleeve,

(iii) a manually rotatable shaft rotatably supported in the bore of said sleeve and having an inner end projecting into said recess, and

(iv) eccentric means on said shaft inner end engaging said pack for reciprocating the latter between its work holding and release positions upon manual rotation of said shaft.

5. The magnetic chuck of claim 4 in which `said shaft has anouter end located exteriorly of the outer end of said bearing sleeve for manual engagement, said sleeve has means temporarily to tix it in any one of a pluraltiy of positions of circumferential adjustment, said eccentric means on the inner end of said shaft being crank pin means mounted eccentrically thereon while extending inward substantially parallel to the shaft axis and a slide block is movably mounted in a slot in the opposed side of said pack for reciprocation in a direction generally normal to said pack face with said block being connected to said crank pin means for reciprocation by rotation of said shaft.

6. In a magnetic chuck of the permanent magnet type, comprising (a) a chambered base structure having a lateral recess therein defined by a later-al bottom wall and pairs of opposed sidewalls and end walls with said recess being covered by (b) a work supporting faceplate structure including transvereSly-extending, laterally-spaced paramagnetic pole piece bars and having .an inner flat face,

(c) an elongated magnetic pack of the permanent magnet type movably mounted in said recess for straight line longitudinal reciprocation therein between work holding and work release positions relative to said faceplate and having opposite longitudinally-extending side edges, a bottom portion and a top flat face opposed to said inner flat face of said faceplate for relative sliding action and (d) means to reciprocate said pack between the work holding and work release positions; the improvement comprising (e) cooperative reciprocation guiding means in the form of interiitting sliding means extending in the direction of longitudinal straight line motion of said pack carried by said opposed faces of said faceplate and pack with the side edges and bottom portion of the latter being free of sliding frictional contact with the opposed sidewalls and bottom wall of -said base structure recess,

7. The magnetic chuck structure of claim 6 in which said interfitting sliding means is in the form of channel means in one of said opposed faces and projecting means on the other of said opposed faces riding in said channel means.

8. The magnetic chuck structure of claim 7 in which said channel means are aligned, longitudinally-spaced groove sections in the inner face of said faceplate and said projection means include lat least one wear -resisting pin extending upwardly from and fixed to the top face of said pack riding in each of said groove sections.

9. In a magnetic chuck of the permanent magnet type the combination with (a) a chambered base structure having an elongated lateral recess therein defined by pairs of opposed sidewalls and end walls and covered by (b) a work supporting faceplate structure including transversely-extending, laterally-spaced paramagnetic pole piece bars and having an inner flat face, and

(c) an elongated magnetic pack of the permanent magnet type movably mounted in said recess for straight line longitudinal reciprocation therein between work holding and work release positions relative to said faceplate having opposite longitudinally-extending side edges and a top at face 4opposed to said faceplate inner face for relative sliding action; of

(d) means to reciprocate said pack between the work holding and work release positions comprising (e) means defining a cylindrical bore extending transve-rsely through one of the sidewalls of said base structure recess,

(f) a cylindrical bearing sleeve rotatably mounted in said hole and having an outer end engageable from the exterior of said casing base structure for rotating said bearing sleeve to a circumferentially adjusted position adjusted position, said sleeve having a cylindrical through bore eccentrically located therein with respect to the cylindrical outer surface of said sleeve.

(g) a manually rotatable shaft rotatably supported in the bore of said sleeve and having an inner end projecting into said recess, and

(h) eccentric means on said shaft inner end engaging said pack for reciprocating the latter between its work holding and release positions upon manual rotation of said shaft. 10. The magnetic chuck structure of claim 9 in which said shaft has an outer end located exteriorly of the outer end of said bearing sleeve for manual engagement, said sleeve has means temporarily to fix it in any one of a plurality of positions of circumferential adjustment, said eccentric means on the inner end of said shaft being .a slide block movably mounted in a substantially vertical slot formed in the opposed side edge of said pack, means defining a transverse bearing hole in one of said slide block and the adjacent inner end of said shaft and a crank pivot pin carried by the other of said slide block and shaft inner end rotatably mounted in said bearing hole with the common axis of this pin and bearing hole being offset radially from the axis of said shaft.

11, A magnetic chuck of the permanent magnet type comprising, in combination with (a) a one-piece casing pan of diamagnetic material deiining a rectangular chamber recess therein flanked by opposed sidewalls and end walls, v

(b) a rectangular work supporting faceplate mounted on said base pan and covering the recess therein to form a closed chamber, said faceplate including an assembly of laterally-spaced paramagnetic pole piece bars for transfer of magnetic lines of force to and from a workpiece resting thereon and having a flat lateral bottom face, and

(c) a rectangular magnetic pack in the form of an assembly of laterally-spaced permanent magnet bars and having pairs of opposite side and end edges spaced inwardly from the chamber sidewalls and end walls for longitudinal reciprocation in the chamber free of sliding contact with said sidewalls between a lateral work holding position of its magnet bars relative to said faceplate pole piece bars to supply to and receive from different ones of the latter magnetic lines of iiux shunted through a supported workpiece and a work release position in which the magnetic lines of force are shunted directly through each faceplate bar,

said pack having a keeper of paramagnetic material 1 carried by the bottoms of said magnet bars as a shunt and a at lateral top face opposed to said faceplate bottom face for relative sliding action; of the improvements comprising (aa) slide promoting means in the form of longitudinally-extending and transversely-spaced anti-friction thin strips of a peruoroalkane resin interposed between said opposed faces and anchored to one thereof While being free of the other for relative slide,

(bb) guide means defining longitudinally-extending channel sections in said faceplate bottom face between locations of said anti-friction strips and guide pins carried by said pack top face between said strips extending upward into the channel sections riding freely therein to limit reciprocation of said pack to straight line motion, and

(cc) means to reciprocate said pack in the chamber relative to said faceplate including a cylindrical bearing sleeve rotatably mounted in a transverse hole extending through one of said chamber sidewalls having an eccentric bore extending longitudinally therethrough with the outer end of said sleeve accessible exterior of said sidewall for angular adjustment in the transverse hole, means defining an upwardly-extending slot in a side edge of said pack opposite said sleeve, a slide block mounted in said slot for free up and down movement, a pack-reciprocating shaft journaled in the sleeve bore and having an inner end opposed to said slide block and an eccentric pin connecting said slide block to said shaft inner end at a point radially of the axis of the latter.

(References on following page) 13 14 References Cited 2,795,740 6/1957 Bohli et a1 335-295 2,815,252 12/1957 Baker 30a-238x UNITED STATES PATENTS 3,151,051 9/1964 Grimm. 2,319,270 5/1943 simmons 269-85( 2,347,023 4/1944 Beecmyn 269-85( 5 ROBERT C. RIORDONJrimdfy Examiner- 2,609,430 9/1952 Bower 269-8X EZRA SUTTON, Assistant Examiner.

UNTTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,336 ,551 August l5 1967 Clifford Stead It is hereby,T certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 29 for "suporting" read supporting column 4, line 73, for the" read these column 5, line I8, for "undersood" read understood line 35 for "the" first occurrence, read and line 49, for "receivig" read --receiving line 73, for "transverse" read traverse H; column 7, line i8, for "thickness" read thicknesses column 9, line 20, for assemby" read assembly column l0 line 16 strike out "being" line 38, for "and" read for ;`line 49, for "casing structure read casing base structure" line 56, for locater" read located columnll, yline l2, for "transveresly" read transversely line 68, strike out "adjusted position" line 70 for "sleeve read sleeve,

Signed and sealed this l3th day of August 1968.

(SEAL) Attest:

EDWARD M.ELETCHER,JR. EDWARD J BRENNER Attesting Officer Commissioner of Patents 

1. IN A MAGNETIC CHUCK OF THE PERMANENT MAGNET TYPE, COMPRISING (A) A CASING BASE STRUCTURE HAVING A RECESS THEREIN DEFINED BY AN INSIDE BOTTOM WALL AND INSIDE SIDEWALLS, (B) A WORK SUPPORTING FACEPLATE MOUNTED ON SAID BASE STRUCTURE AND COVERING THE RECESS THEREIN WITH SAID FACEPLATE INCLUDING AN ASSEMBLY OF LATERALLY-SPACED POLE PIECES OF PARAMAGNETIC MATERIAL, AND FACEPLATE HAVING AN INNER FACE ARRANGED SUBSTANTIALLY IN A LATTERAL PLANE, (C) A MAGNETIC PACK OF THE PERMANENT MAGNET TYPE RECIPROCATIVELY MOUNTED FOR LATERAL MOVEMENT IN SAID RECESS FREE OF ANY CONTACT WITH ANY OPPOSED PORTIONS OF SAID BOTTOM AND SIDE WALLS DEFINING THE LATTER, WITH SAID PACK INCLUDING AN ASSEMBLY OF LATERALLY-SPACED PERMANENT MAGNETS COOPERATIVELY ARRANGED WITH RESPECT TO SAID FACEPLATE POLE PIECES IN A LATERAL WORK HOLDING POSITION OF SAID PACK WITH SAID PACK HAVING A FACE DISPOSED IN A SUBSTANTIALLY LATERAL PLANE OPPOSED TO SAID INNER FACE OF SAID FACEPLATE FOR LATERAL RECIPROCATION RELATIVE TO THE LATTER, AND (D) MEANS TO RECIPROCATE SAID PACK LATERALLY BETWEEN THE WORK HOLDING POSITION AND ANOTHER POSITION OF WORK RELEASE RELATIVE TO SAID FACEPLATE POLE PIECES; THE IMPROVEMENT COMPRISING (E) MEANS GUIDING FREE RECIPROCATION OF SAID PACK IN THE BASE STRUCTURE RECESS WHICH ELIMINATES ANY FRICTIONAL SLIDING CONTACT BETWEEN ANY PORTIONS OF AND FIXEDLY MOUNTED ON THE NSIDE BOTTOM AND SIDE WALLS OF THE BASE STRUCTURE RECESS AND OPPOSED PORTIONS OF SAID PACK, AND (F) SLIDE PROMOTING MEANS INTERPOSED BETWEEN SAID FACEPLATE AND PACK OPPOSED FACES SPACING THEM A MINIMUM DISTANCE APART COMPRISING THIN, TOUGH, LONG WEARING DIAMAGNETIC PLASTIC SHEETING OF LOW FRICTION AND HIGH LUBRICITY, WHILE MAGNETIC ATTRACTION BETWEEN SAID FACEPLATE AND PACK MAINTAIN THE OPPOSED FACES OF SAID FACEPLATE AND PACK URGED TOWARD EACH OTHER ON OPPOSITE SIDES OF SAID PLASTIC SHEETING. 